Loft Boarding Load Calculator
Instantly estimate the safe weight capacity of your loft for boarding and storage. Accurate, free joist span and load calculator for UK homes.
Calculate Safe Loft Load
Enter your loft’s joist specifications below to get an estimated safe load capacity for storage boarding.
Loft Load Estimator
Enter your joist details to calculate capacity
Estimated Capacity
Based on standard UK timber guidelines
Common Joist Load Capacities
General guidelines for typical UK loft joist configurations (assuming a 3-metre span and 400mm spacing).
| Joist Size | Est. Safe Load (kg/m²) | Suitable For |
|---|---|---|
| 100 x 50 mm | 25 – 40 kg/m² | Light access only, minimal storage |
| 125 x 50 mm | 50 – 75 kg/m² | Light storage, seasonal decorations |
| 150 x 50 mm | 100 – 125 kg/m² | General household storage, boxes |
| 200 x 50 mm | 150 – 200 kg/m² | Heavy storage, water tanks, archives |
| 225 x 50 mm | 200+ kg/m² | Maximum storage, potential room conversion base |
Loft Boarding FAQ
Everything you need to know about safely boarding your loft for storage.
A standard UK loft designed only for access (with 100x50mm joists) is typically rated for about 25 kg per square metre. If upgraded with larger joists (e.g., 150x50mm or 200x50mm) and proper boarding, it can safely hold 100 to 150+ kg per square metre for storage.
You can board over 100x50mm joists, but only for very light storage. These joists are primarily designed to support the ceiling below and allow occasional access. For heavy boxes or water tanks, you must install additional ‘over-joists’ (e.g., 100x50mm or 150x50mm) to raise the boarding and prevent ceiling sagging.
If you are only adding lightweight boarding for storage and not converting the loft into a habitable room, you generally do not need Building Regulations approval. However, the structure must still be capable of safely supporting the added load without compromising the ceiling below.
For standard joist spacing of 400mm, 18mm or 22mm chipboard/OSB is commonly used. For 600mm joist spacing, 22mm or 25mm tongue-and-groove (T&G) boards are recommended to prevent flexing and ensure a safe, rigid walking surface.